Commit Message

From: Andres Salomon <dilinger@queued.net>
I've noticed some pretty poor behavior on OLPC machines after bootup, when
gdm/X are starting. The GCD monopolizes the scheduler (which in turns
means it gets to do more nand i/o), which results in processes taking much
much longer than they should to start.
As an example, on an OLPC machine going from OFW to a usable X (via
auto-login gdm) takes 2m 30s. The majority of this time is consumed by
the switch into graphical mode. With this patch, we cut a full 60s off of
bootup time. After bootup, things are much snappier as well.
Note that we have seen a CRC node error with this patch that causes the machine
to fail to boot, but we've also seen that problem without this patch.
Signed-off-by: Andres Salomon <dilinger@debian.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
fs/jffs2/background.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff -puN fs/jffs2/background.c~jffs2-force-the-jffs2-gc-daemon-to-behave-a-bit-better fs/jffs2/background.c--- a/fs/jffs2/background.c~jffs2-force-the-jffs2-gc-daemon-to-behave-a-bit-better+++ a/fs/jffs2/background.c@@ -95,13 +95,17 @@ static int jffs2_garbage_collect_thread(
spin_unlock(&c->erase_completion_lock);
- /* This thread is purely an optimisation. But if it runs when- other things could be running, it actually makes things a- lot worse. Use yield() and put it at the back of the runqueue- every time. Especially during boot, pulling an inode in- with read_inode() is much preferable to having the GC thread- get there first. */- yield();+ /* Problem - immediately after bootup, the GCD spends a lot+ * of time in places like jffs2_kill_fragtree(); so much so+ * that userspace processes (like gdm and X) are starved+ * despite plenty of cond_resched()s and renicing. Yield()+ * doesn't help, either (presumably because userspace and GCD+ * are generally competing for a higher latency resource -+ * disk).+ * This forces the GCD to slow the hell down. Pulling an+ * inode in with read_inode() is much preferable to having+ * the GC thread get there first. */+ schedule_timeout_interruptible(msecs_to_jiffies(50));
/* Put_super will send a SIGKILL and then wait on the sem.
*/